Water treatment systems have been in existence for many years. These systems treat stormwater surface runoff or other polluted water. Stormwater surface runoff is of concern for two main reasons: one because of the effects of its volume and flow rate, and two, because of the pollution and contamination it can carry. The volume and flow rate of stormwater is important because high volumes and high flow rates can cause erosion and flooding. Pollution and contamination are important because stormwater is carried into our rivers and streams, from there into our lakes and wetlands, and furthermore because it can eventually reach our oceans. Pollution and contamination that is carried by stormwater can have adverse affects on the health and ecological balance of the environment.
The Clean Water Act of 1972 set the stage for vast improvements to a water infrastructure and quality. Water pollution has been divided into two categories: point source and non-point source. Point sources include wastewater and industrial waste. Point sources are more easily identifiable, and therefore direct measures can be taken to control them. The other category, non-point source, is more difficult to identify. Stormwater runoff is the major contributor to non-point source pollution in rivers, lakes, steams and oceans. Studies have suggested and confirmed the leading cause of pollution to our waterways is from contaminated stormwater runoff. As we build houses, buildings, parking lots, roads and other impervious areas, we increase the amount of water that runs off the land and into our stormwater drainage systems, which all lead to rivers, lakes, streams and the ocean. As more land becomes impervious, less of the rain seeps back into the ground. This leads to less groundwater recharge and higher velocity flows in streams, which cause erosion and increased loads of contaminants into these waterways.
There are numerous sources of pollutants that are present in stormwater runoff. Sediments come from hillsides and other natural areas that are disturbed during construction and other human activities. When land is stripped of vegetation the soil more easily erodes and finds its way to storm drains. Trash and other unnatural debris are dropped on the ground every day which find its ways into the drainage system and ultimately our waterways. Leaves from tress and grass clippings from landscape activities that land on hardscape areas no longer decompose back into the ground but flow to our storm drains and collect in huge concentrations in lakes and streams. These organic substances leach out huge loads of nutrients and they decompose and cause large algae blooms which deplete the dissolved oxygen levels and kill fish and other organisms. Other unnatural sources of nutrients including nitrogen, phosphorus, and ammonia come from residential and agricultural fertilizers that are used in access and find there way to storm drains. Nutrients are one of the number one pollutants of concern in our nations.
Other major pollutants of concern include heavy metals which come from numerous sources and are harmful to fish and other organisms including humans. Many of our waterways are no longer safe to swim in or fish in and therefore no longer have any beneficial use. Heavy metals include but are not limited to zinc, copper, lead, mercury, cadmium and selenium. These metals come from car tires and break pads, paints, galvanized roofs and fences, industrial activities, mining, recycling centers, any metal materials left uncovered. Other major pollutants of concern are hydrocarbons which include oils & grease. These pollutants come from leaky cars and other heavy equipment and include hydraulic fluid, break fluid, diesel, gasoline, motor oils, cooking oils and other industrial activities.
Bacteria, pesticides and organic compounds are a few other categories of pollutants which are also harmful to our waterways, wildlife and humans. Over the last 20 years the EPA has been monitoring the pollutant concentrations in most of the streams, rivers and lakes throughout the country. Over 50% of our waterways are impaired for one of more of the above mentioned pollutants. As part of the Phase 1 and Phase 2 NPDES permits which control industrial and non-industrial development activities the control of these sources of pollutants in now mandated. Phase 1 was initiated in 1997 and Phase 2 was initiated in 2003. While there are many requirements to these permits the three main focuses are on source control, during construction pollution control and post construction pollution control. Post construction control mandates that any new land development or redevelopment activities are required to incorporate methods and solutions that both control increased flows of rain water off the site and decrease (filter out) the concentration of pollutants off of these developed sites. These are commonly known as quantity and quality control. Another part of the these requirements is for existing publicly owned developed areas to retrofit the existing drainage infrastructure with quality and quantity control methods and technologies to decrease the existing amount of rain water runoff and pollutant concentrations.
One of the main categories of technology that help with obtaining these goals are referred to as structural best management practices or BMPs. Structural BMPs are proprietary and non-proprietary technologies that are developed to store and/or remove pollutants from stormwater. Methods such as detention ponds, regional wetlands are used to control the volume of runoff while providing some pollutant reduction capabilities. Over the past 10 years numerous technologies have been invented to effectively store water underground and thus freeing up buildable land above them. Various treatment technologies such as catch basin filters, hydrodynamic separators, media filters are used to remove pollutants. These technologies commonly work by using the following unit processes: screening, separation, physical filtration and chemical filtration.
Other technologies such as bio swales, infiltration trenches, and bioretention areas commonly known as low impact development (LID) or green technologies have recently been implemented in the last 10 year to both control flow volumes and remove pollutants on a micro level. These LID technologies have proven successful at removing difficult pollutants such as bacteria, dissolved nutrients and metals as they provide not only physical and chemical, but also biological filtration processes by incorporating a living vegetation element which creates a living microbial community within the media by the plants root systems which assist in pollutant removal. Biological filtration processes have proven to be excellent at removing many of the pollutants that physical and chemical filtration systems alone cannot. While these technologies are effective they take up substantial amounts of space which are not always available on various construction projects. As such a need has arisen for compact LID technologies that offer the same advantages as their larger and space expensive counterparts.
Recent technology advancements in the field have focused on taking the traditional bioretention concept which is focused around vertical downward flow media filtration beds that pond water on top of the bed and making them up to 10th of the size smaller by using high flow rate filtration media. As with traditional large bioretention systems these new compact bioretention systems accept stormwater runoff directly without pre-treatment and therefore receive large amounts of particulates that can clog the media filtration bed. This clogging as been exacerbated with these compact systems as the surface area of the media is only one tenth that of the traditional large bioretention systems. These downward flow systems are notorious for clogging as sediments accumulate on top of the media filtration beds surface. The need for a better way of making biofiltration system which allows the systems to still be compact but maximizes the media surface area for a given media bed volume. The greater the surface area for a given volume of bed media the lower the loading rate on the media and therefore less probability of clogging. Also, the traditional downward vertical flow path through a media bed is the most problematic for clogging as gravity allows inflow particulates to quickly and easily accumulate on top of the media bed.
Stormwater is characterized by large concentrations of various pollutants including trash, debris and sediments. Reports have shown that for urbanized area an average of 7.6 cubic feet of trash and 2.4 cubic yards of sediment are generated per acre of impervious surface per year. In many areas, where proper erosion control measures are not taken, which is common, the loading of sediment is much higher. Therefore, a system which has a media bed designed to minimize clogging along with a pre-treatment chamber to remove trash and sediments provides huge advantages to the end user. The maintenance of all stormwater BMPs can be very expensive and a burden to property owners. There is, thus a need to a system that can minimize maintenance costs.
Also, with changing stormwater regulations, a move is being made from flow based design to volume based design. Volume based design requires treatment along with volume control. Volume based design requires not only a treatment system but a storage system. Only horizontal flow media bed filters that included live vegetation can be placed downstream of the storage system. By having the vegetated media bed filter down stream allows it to also provide the flow control. This eliminates the need for a separate flow control structure which is costly. Having the media bed filter downstream also allows the water to be metered through the system over an extending period of time as a much slower flow rate when compared to flow based design. This further reduces the surface area loading rate which further minimizes clogging and also drastically increases the hydraulic retention time. The longer the retention time the higher the performance ability of the system.
Some systems include a wetlands chamber having a vegetative submerged bed, one or more walls, a floor, one or more inlet water transfer pipes and one or more outlet water transfer pipes. Examples of related systems are described in U.S. Pat. No. 7,425,262 B1, U.S. Pat. No. 7,470,362 B2 and U.S. Pat. No. 7,674,378, the contents of each of which are incorporated herein by reference in their entirety. In other systems, each of the walls and floor have an inner and outer metal mesh wall, with a space between the inner and outer walls to house stonewool filtration media slabs. Having a catch basin or chamber also includes one or more inflow pipes in one or more of the four walls to allow influent to pass into the catch basin. The system is configured so that the sediments and associated pollutants settle out of the influent and accumulate on the floor of the catch basin or chamber. A filtration panel comprising four or more walls enclosing an open space housing a filtration media, the walls being water permeable in structure to allow passage of water in either direction, the filtration media filling the entire inner chamber of the filtration panel and being water permeable.
Contaminated water such as stormwater and waste water contain high levels of particulate pollutants such as TSS, metals, organics, nutrients and hydrocarbons. These particulates cause media filtration beds to clog, which decreases their treatment flow capacity and increases the maintenance and replacement requirements of the granular media within the media filtration bed. Because of this a need has arisen that further increases the amount of initial media bed surface area for a given volume of filter media. By increasing the amount of available media bed surface area for a given volume of media the surface loading rate decreases for a given flow of water and therefore decreases the rate at which media will clog due to particulates.
Traditional downward flow media filtration beds have their initial media surface area lay horizontal perpendicular with the force of gravity. Therefore, pollutant particles accumulate on top of the media bed and clog the media at a much faster rate and thereby decreasing the media filtration bed's flow rate and performance, along with increasing the required maintenance and decreasing the life of the media before replacement is needed.
With the ever changing stormwater regulations a system that provides features that lowers maintenance costs, increases performance and pollutant removal and can be integrated with storages systems and placed downstream are in great need and demand. The smaller these systems are the easier they can be integrated into urban areas with limited room. The easier it is made to incorporate these systems in urban areas the greater overall affect we will have at reducing pollution to our precious rivers, lakes and streams.